1. Field of the Invention
The embodiments discussed herein are related to a semiconductor device.
2. Background of the Related Art
A power semiconductor module, which is a semiconductor device, includes a switching element made of silicon (Si) and a diode element made of a wide-band-gap semiconductor, such as silicon carbide (SiC), and is used as a power converter. With such a semiconductor device, a laminated substrate formed by laminating a circuit board, an insulating board, and a metal board is joined to a cooling plate made of metal by the use of solder. In addition, semiconductor elements, such as the above switching element or diode element, are disposed over the circuit board of the laminated substrate.
In this case, compared with the Si switching element, the SiC diode element is small in loss, operates stably at high temperatures, and has a high withstand voltage. The SiC diode element has these characteristics. Therefore, diode elements are disposed in a central area in the semiconductor device. In the central area in the semiconductor device, it is difficult to radiate heat, and therefore temperature tends to rise. Switching elements are disposed around the central area. This improves efficiency in the cooling of the semiconductor device (see, for example, Japanese Patent No. 5147996).
With the above semiconductor device (see, for example, Japanese Patent No. 5147996), cracks may appear in corner portions of the solder under the laminated substrate as a result of a heat cycle. When a heat cycle is repeated, the crack expands from each corner portion of the solder towards the center portion. Accordingly, the crack goes under a switching element made of silicon and disposed over a corner portion. Furthermore, the crack contains air. As a result, when heat is conducted from the switching element through the laminated substrate to the cooling plate, the crack in the solder degrades the heat radiation property. Compared with the SiC diode element, it is difficult for the Si switching element to operate stably at high temperatures. In this case, the heat radiation property of the Si switching element is degraded. This may lower the reliability of the semiconductor device.